1. Field of the Invention
The present invention is in the field of mixing devices used to create an emulsion, such as a device used to create an appropriate oil and water emulsion, in preparation for desalting and dewatering of an oil-continuous emulsion such as crude petroleum.
2. Background Information
An oil-continuous emulsion such as crude petroleum can be desalted and dehydrated by introduction of the emulsion into an electric field. The electric field will coalesce suspended droplets of the dispersed water phase, in which the salts are contained, into larger masses of salty water. The larger masses of water and salt will then gravitate from the emulsion, leaving the oil phase. The incoming crude oil typically contains some water and salt. It is typical to add water, to arrive at a water concentration of approximately 10%, and then mix the added water with the oil emulsion in a mixing device, to create a more complete emulsion of salty water and oil. This makes possible the more complete removal of salt from the oil by the electric field.
Mixing of the added water into the incoming emusion of oil and salty water is normally accomplished by pumping these components through a valve, prior to introduction of the emulsion into the electric field. In the mixing valve, the oil, salty water, and added water flow through restricted areas which create fluid shear forces to accomplish the mixing. Currently known valves used for this purpose are typically valves which were originally designed for use as control valves, rather than mixing devices. Such valves have been adapted for the mixing application because they have one or more valve discs which can be positioned in proximity to one or more respective valve seats, with the valve in a partially open position, thereby creating fluid shear forces as the fluids flow through the restricted areas between the discs and the seats. The fluid shear thusly created mixes the component fluids in a more complete emulsion.
Unfortunately, since the currently known mixing valves were originally designed as control valves, rather than mixing devices, they suffer from some disadvantages. The primary disadvantage is that, in the known mixing valves, the design of the discs, seats, and valve flow paths results in the creation of higher than necessary flow resistance. This is because a control valve is designed to control flow rates by creating flow resistance through several means, only one of which is the creation of fluid shear. Various structural elements in a typical control valve, such as the portions of the valve plug in the flow path and the flow channels in the valve body, create additional flow resistance. In these valves, the proportion of flow resistance that results from structural elements other than the fluid shear-creating elements is relatively high. This means that additional pump capacity, along with its additional capital cost and operating cost, is necessary, to achieve a given flow rate. It would be desirable to have an emulsifying device in which almost all of the flow resistance results from the fluid shear-creating elements of the device.
A second disadvantage of the currently known mixing valves is that they tend to be larger and heavier than necessary. In the typical such valve, the surfaces which actually create fluid shear forces, namely the disc and seat surfaces, tend to occupy the central region of the valve body cavity, with peripheral valve body areas being necessarily devoted to flow channeling structures. This means that, not only is the valve large, heavy, and complex, but the total shear-creating surface area has not been optimized. It would be desirable to have an emulsifying device in which the surface utilized for creating fluid shear is as large as possible for a given size body, with the shear-creating surfaces ideally occupying the peripheral portion of the valve body cavity, rather than only the central portion.